Re: [PATCH] target/riscv: Do not hide Sstc CSRs from gdbstub

[Chao Liu <chao.liu.zevorn@gmail.com>]

On Mon, May 25, 2026 at 10:42:20AM +0800, Zephyr Li wrote:
> The Sstc predicate currently checks both ext_sstc and rdtime_fn. This
> causes the gdbstub CSR XML generation to skip Sstc CSRs when rdtime_fn
> has not been initialized yet, even if the CPU supports Sstc.
> 
> As a result, GDB reports $stimecmp as void with a CPU that exposes the
> sstc extension.
> 
> Only use ext_sstc for the early existence check, and keep the rdtime_fn
> check for non-debugger accesses.
> 
> Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3496
> Signed-off-by: Zephyr Li <fritchleybohrer@gmail.com>

Reviewed-by: Chao Liu <chao.liu.zevorn@gmail.com>

> ---
> 
> Testing:
>     Start QEMU with:
>         qemu-system-riscv64 -M virt,aclint=on -cpu max,sstc=true -s -S -nographic
> 
>     Before:
>         (gdb) p $stimecmp
>         $1 = void
> 
>     After:
>         (gdb) p $stimecmp
>         $1 = 0
> 
>  target/riscv/csr.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/target/riscv/csr.c b/target/riscv/csr.c
> index da366cf562..c17df147f7 100644
> --- a/target/riscv/csr.c
> +++ b/target/riscv/csr.c
> @@ -586,7 +586,7 @@ static RISCVException sstc(CPURISCVState *env, int csrno)
>  {
>      bool hmode_check = false;
>  
> -    if (!riscv_cpu_cfg(env)->ext_sstc || !env->rdtime_fn) {
> +    if (!riscv_cpu_cfg(env)->ext_sstc) {
>          return RISCV_EXCP_ILLEGAL_INST;
>      }
>  
> @@ -603,6 +603,10 @@ static RISCVException sstc(CPURISCVState *env, int csrno)
>          return RISCV_EXCP_NONE;
>      }
>  
> +    if (!env->rdtime_fn) {
> +        return RISCV_EXCP_ILLEGAL_INST;
> +    }
> +
>      if (env->priv == PRV_M) {
>          return RISCV_EXCP_NONE;
>      }
> -- 
> 2.43.0
>